CN115698558A

CN115698558A - Improved sealing device for hydraulic machine

Info

Publication number: CN115698558A
Application number: CN202180037300.5A
Authority: CN
Inventors: J·昂格朗; G·格里永; S·奎特莱
Original assignee: Poclain Hydraulics Industrie
Current assignee: Poclain Hydraulics Industrie
Priority date: 2020-05-25
Filing date: 2021-05-10
Publication date: 2023-02-03
Also published as: WO2021240090A1; FR3110659A1; FR3110659B1; US20230193885A1; JP2023526559A; EP4158225A1

Abstract

Hydraulic machine (1) comprising a first assembly (10) and a second assembly (20) which are movable in rotation with respect to each other along a rotation axis (X-X), said machine (1) comprising a crankcase defining an internal volume (2), wherein the interface between the fixed and movable assemblies comprises a casing (4) provided with a first sealing element (40) ensuring the sealing of the internal volume (2) with respect to the external environment, characterized in that a second sealing element (6) is located between the internal volume (2) and the casing (2), said second sealing element (6) being adapted to allow the flow of fluid from the internal volume (2) to the casing (4) when the pressure deviation between the internal volume (2) and the casing (4) is less than or equal to a threshold value and to isolate the casing (4) from the internal volume (2) when said pressure deviation is greater than said threshold value.

Description

Improved sealing device for hydraulic machine

Technical Field

The present invention relates to an improved seal for a hydraulic machine and, more particularly, to a seal protector against peak pressures.

Background

The use of rotating machinery in different environments creates sealing problems. In fact, one recurring problem is preventing impurities from entering the internal volume of the crankcase (crankcase) of the rotary machine.

In order to ensure a good seal between the internal volume of the rotary machine and the external environment, different sealing structures have been proposed. However, the known solutions still present problems in terms of reliability, in particular over time.

A first mounting is to place a single sealing element to ensure isolation between the surrounding environment and the interior volume of the crankcase. However, in the case of elevated pressures in the crankcase, the sealing element may be pushed out of its housing or broken due to increased bearing forces between the two sliding parts, for example due to tearing or seizing (sizing) of the surfaces in sliding contact in the case of a metal seal. In the case of metal seals, this leads to high friction and loss of efficiency. This pressure rise in the crankcase is, for example, due to the start-up of a cold hydraulic machine. The pressurized oil reaches the crankcase of the machine, through conventional internal leakage in these machines, whereas the crankcase oil cannot easily escape through the crankcase drain pipe, which is still filled with cold oil, thus creating a very high pressure drop due to the high viscosity of the cold oil. This operation can quickly damage the sealing element. In particular, if the pressure in the crankcase of the machine rises, the bearing force between the sliding parts of the sealing element increases and in the case of a flexible sealing element jamming or squeezing may occur, which will destroy the sealing element. The components of the sealing element may also be damaged by the pressure.

Alternatively, the anti-contamination sealing elements ensuring the isolation between the ambient environment and the internal volume of the crankcase may be provided in dedicated housings, which are themselves isolated from the internal volume of the crankcase comprising the rotating machine (e.g. hydraulic machine) by means of crankcase seals (usually called absolute seals), associating the dynamic sealing elements (e.g. lip rings) with dynamic sealing elements (e.g. O-rings connected to the ring elements) which are resistant to possible peak pressures. However, such mounting thus defines a closed chamber between the axial and crankcase sealing elements. However, such closed chambers create problems with regard to lubrication. In fact, the housing comprising the axial sealing element is completely isolated from the internal volume of the crankcase by the crankcase seal, which is not continuously lubricated, in particular in case lubricant is lost over time or its properties deteriorate. However, the lack of lubrication can lead to rapid deterioration of the sealing elements, particularly under the influence of seizing or squeezing due to lack of oil, a commonly proposed solution consists in injecting a predetermined amount of oil into the casing, which must be replaced regularly. The housing must also have sufficient volume which makes the hydraulic machine less compact. However, it should be understood that this solution is highly restrictive and requires special maintenance operations.

The present invention is therefore directed to at least partially solve these problems.

Disclosure of Invention

To this end, the invention relates to a hydraulic machine comprising a first assembly and a second assembly that are rotationally movable relative to each other along a rotation axis, the hydraulic machine comprising a crankcase defining an internal volume,

wherein the interface between the fixed component and the mobile component comprises a housing provided with a first sealing element to ensure the sealing of the internal volume with respect to the external environment,

characterized in that a second sealing element is located between the inner volume and the housing, the second sealing element being adapted to allow fluid flow from the inner volume to the housing when a pressure deviation between the inner volume and the housing is less than or equal to a pressure threshold value, and to inhibit fluid flow from the inner volume to the housing when the pressure deviation between the inner volume and the housing exceeds the threshold value by more than said pressure threshold value.

According to one example, the second sealing element comprises a passage adapted to be closed when the pressure in the inner volume or the housing exceeds a threshold value, or for example when the pressure difference between the inner volume and the housing exceeds a threshold value (typically 0.1 bar, 0.2 bar or 0.5 bar).

According to one example, the first sealing element is an axial seal comprising a first metal ring (annulus), a second metal ring, a first elastic ring and a second elastic ring, the first metal ring and the second metal ring being mounted against each other in an axial direction defined by the axis of rotation, the first elastic ring being interposed between the first metal ring and a wall of the first component and the second elastic ring being interposed between the second metal ring and a wall of the second component.

According to one example, the second sealing element comprises an O-ring (ring).

The second sealing element then typically comprises a ring on which an O-ring is mounted.

The ring then typically includes an aperture that allows fluid to pass when the pressure deviation between the internal volume and the housing is less than or equal to the pressure threshold and does not allow fluid to pass when the pressure deviation between the internal volume and the housing is greater than the pressure threshold.

According to one example, the second sealing element is located between the two rolling elements, ensuring a relative rotational movement between the first and second assemblies.

According to one example, the second sealing element is made in one piece.

According to one example, the second sealing element is adapted to allow fluid to flow from the housing to the internal volume when a pressure deviation between the internal volume and the housing is less than or equal to a pressure threshold value, and to allow isolation of the housing from the internal volume when the pressure deviation between the internal volume and the housing is greater than the pressure threshold value.

According to one example, the second sealing element is interposed between two surfaces facing each other in an axial direction defined by the rotation axis.

According to one example, the second sealing element is interposed between two surfaces facing each other in a radial direction with respect to the rotation axis.

According to one example, the pressure threshold is equal to 0.5 bar, or 0.2 bar, or even 0.1 bar.

A hydraulic machine is, for example, a machine comprising a cylinder block having a plurality of housings extending radially with respect to an axis of rotation, in which the cylinders are arranged, and a multi-lobed cam which surrounds the cylinder block.

Drawings

The invention and its advantages will be better understood by reading the following detailed description of the different embodiments of the invention, given by way of non-limiting example.

FIG. 1 shows a general view of one example of a hydraulic machine according to one aspect of the present invention.

FIG. 2 shows an example of a hydraulic machine according to one aspect of the present invention.

FIG. 3 is a detailed view of a sealing element according to one aspect of the present invention.

FIG. 4 is a detailed view of a sealing element according to one aspect of the present invention.

FIG. 5 is a detailed view of a sealing element according to one aspect of the present invention.

FIG. 6 shows an example of a hydraulic machine according to one aspect of the present invention.

FIG. 7 shows an example of a hydraulic machine according to one aspect of the present invention.

Common elements are identified by the same reference numerals throughout the drawings.

Detailed Description

An exemplary embodiment of the present invention is described below with reference to fig. 1 to 5.

Fig. 1 is a cross-sectional view of a hydraulic machine 1, typically a radial piston and multi-lobe cam (multilobe-cam) hydraulic machine. Since hydraulic machines are usually referred to as hydraulic motors or pumps, these devices usually have reversible operation. The hydraulic machine 1 comprises a distributor cover 110, a feed distributor 112, an assembly comprising a cylinder block 114 and a piston 116 equipped with bearing rollers 118 (commonly known as hydrodynamic torque), a multi-lobed cam 120, a shaft 122 and bearing 124 consisting of bearing assemblies, and a bearing cover 126. The shaft 122 is mechanically connected to the cylinder 114 to transmit rotational motion resulting from torque applied to the shaft 122 or sliding of the piston 116 in contact with the multi-lobed cam 120. The distributor cap 110 comprises a supply conduit for the intake and delivery of the hydraulic machine 1. The suction and delivery conduits, the conduits of the distributor and the piston chamber of the cylinder are connected to a hydraulic power circuit which transmits hydraulic power. For example, it is connected to the supply and return branches of the closed-loop hydraulic circuit, or to the high-pressure HP and low-pressure LP branches, or to the supply line via a power pump, and to the return line leading to the tank for the open-loop hydraulic circuit. In the example shown, the distributor cover 110, the cam 120 and the bearing cover 126 define a crankcase of the hydraulic machine 1.

The volume contained in the crankcase around the different elements mentioned above represents the internal volume of the hydraulic machine 1. Which is indicated by shading in fig. 1. Which is isolated from the hydraulic power circuit (represented by dotted lines) by the sealing of the piston 116 and the distributor 112 in a manner known to those skilled in the art. The internal volume of the hydraulic machine 1 receives a flow of oil leaking from the inside of the hydraulic machine 1, coming from the power circuit, and is normally connected to a tank through a drain to drain it, so that the pressure in the internal volume of the hydraulic machine 1 remains substantially equal to the pressure of said tank, which is normally equal to or close to atmospheric pressure.

Figure 2 is a partial cross-sectional view of the hydraulic machine 1. The hydraulic machine 1 comprises a first assembly 10 and a second assembly 20, which are movable in rotation with respect to each other along a rotation axis X-X. In the following description, the terms "radial" and "axial" are defined with respect to the axis of rotation X-X unless otherwise indicated.

In the example shown, the rotational movement is ensured by rolling elements, here

conical bearings

32 and 34 forming the bearing 30. The hydraulic machine 1 comprises an internal volume 2 in which various components 3 of the machine, according to their nature, are arranged, such as radial piston or axial piston hydraulic motors, radial piston or axial piston hydraulic pumps, braking systems or any other device.

The first assembly 10 and the second assembly 20 represent different parts of the hydraulic machine. By way of example, one of these assemblies may comprise a shaft, cylinder and dispenser of a hydraulic machine, while another of these assemblies may comprise a multi-lobed cam. The first assembly 10 and the second assembly 20 may comprise braking means, such as discs, adapted to prevent relative rotational movement of the first assembly 10 with respect to the second assembly 20 under the effect of friction between said discs.

The internal volume 2 of the hydraulic machine is isolated from the external environment by a first sealing element 40 provided in the casing 4. The housing 4 is connected to the external environment through a duct 5 formed by the gap between the first component 10 and the second component 20. In the example shown, the first sealing element 40 is an axial seal or a floating seal, commonly referred to as a double cone seal.

Here, the first sealing element 40 comprises a first metallic ring 41 and a second metallic ring 43 made of metallic material and generally symmetrical with respect to a plane extending radially with respect to the rotation axis X-X. The first sealing element 40 further comprises a first elastic ring 42 and a second elastic ring 44 made of elastomeric material.

The first metallic ring 41 and the second metallic ring 43 abut against each other in the axial direction defined by the rotation axis X-X.

The first elastic ring 42 is mounted against the first metal ring 41 on the one hand and against the partition 14 of the first assembly 10 on the other hand.

The second elastic ring 44 is mounted against the second metal ring 43 on the one hand and against the partition 24 of the second assembly 20 on the other hand.

The first elastic ring 42 and the second elastic ring 44 are generally located radially outward relative to the first metallic ring 41 and the second metallic ring 43. The first metal ring 41 and the second metal ring 43 press the first elastic ring 42 and the second elastic ring 44 against the

diaphragms

14 and 24 of the first assembly 10 and the second assembly 20, respectively, so as to ensure a sealed connection.

The first and second metal rings 41 and 43 and the

diaphragms

14 and 24 of the first and

second assemblies

10 and 20, respectively, are generally formed such that the first and second

elastic rings

42 and 44 tend to move the first and second metal rings 41 and 43 relative to each other along an axial direction defined by the axis of rotation X-X.

As mentioned above, a problem with such mounting relates to lubrication of the first sealing element 40. Indeed, in conventional constructions, the housing 4 is typically isolated from the internal volume of the crankcase 1 by an absolute seal, which generally comprises a dynamic seal coupled to a reinforced seal (e.g., a lip ring) particularly adapted to withstand any peak pressures. However, this mounting completely isolates the housing 4 from the internal volume of the crankcase 1, which therefore requires lubrication to be provided from the design, for example by injecting a predetermined amount of oil into the housing 4. However, as soon as the oil gradually escapes into the external environment, regular maintenance operations are required in order to reintroduce the oil into the casing 4. Furthermore, in the event of peak pressures in the interior volume of the crankcase 1, problems arise with this construction, which can lead to damage of the sealing elements located in the housing 4.

The construction proposed by the invention does not provide a positive seal between the inner volume 2 and the housing 4, but a second sealing element 6. The proposed second sealing element 6 is adapted to allow fluid to flow from the inner volume 2 to the housing 4 when the pressure in the inner volume 2 is less than or equal to a pressure threshold value, and to isolate the housing 4 from the inner volume 2 when a pressure deviation between the inner volume 2 and the housing 4 is greater than said pressure threshold value, such that fluid is not allowed to flow from the inner volume 2 to the housing 4 when the pressure deviation between the inner volume 2 and the housing 4 is greater than said pressure threshold value. The second sealing element 6 thus has the function of a calibration valve or a two-way flow nozzle.

The passage in the second sealing element may also work in the opposite way, allowing oil to flow from the housing into the inner volume when the pressure in the inner volume increases, especially in case of heating. This operation in both flow channels does not impair the lubrication of the housing 4.

Thus, the second sealing element 6 may enable a calibrated flow of oil from the inner volume 2 to the housing 4 when the pressure deviation between the inner volume 2 and the housing 4 is less than or equal to a predetermined pressure threshold. The second sealing element 6 therefore generally has a passage that allows the circulation of fluid between the internal volume 2 and the casing 4 as long as the pressure is less than or equal to a pressure threshold, and closes when the pressure deviation between the casing 4 and the internal volume 2 exceeds the pressure threshold, then isolates the internal volume 2 from the casing 4. More generally, the second sealing element 6 is calibrated so that the flow rate of the fluid that can pass in the housing 4 does not cause an excessive pressure rise in the housing 4. According to an example, the second sealing element may be calibrated to allow the pressure in the housing 4 to rise by approximately 0.2 bar (bar), changing from a pressure of 3 bar to a pressure of 3.2 bar, in this case 3 bar being the value of the pressure in the housing 4 and the internal volume 2 before the peak pressure in the internal volume 2.

This function may thus ensure continuous lubrication of the housing 4 while protecting the first sealing element 40 from peak pressures within the internal volume 2. In fact, in the event of a peak pressure occurring within the internal volume 2, the second sealing element 6 is not electrically conductive and then behaves like an absolute seal, preventing an excessively high pressure, which would lead to a deterioration of the first sealing element 40, from reaching the casing 4.

The pressure threshold is for example between 2.5 bar and 3.5 bar, or more specifically between 3 bar and 3.2 bar. More generally, operation in the conductive or non-conductive mode may depend on the pressure difference on either side of the second sealing element 6, for example when the pressure difference is greater than or equal to 0.5 bar, or greater than or equal to 0.2 bar, or even greater than or equal to 0.1 bar.

In the opposite direction, the second sealing element 6 allows the passage of fluid when the pressure in the internal volume 2 does not exceed the pressure threshold. When heating occurs in the housing 4, the pressure rises slowly and the oil flows towards the inner volume 2 before a peak pressure is generated. In this way, the pressure in the housing 4 does not exceed the pressure of the internal volume 2 as long as the pressure of the internal volume 2 is below the pressure threshold. The housing 4 itself has no possibility of pressure rise. The risk of the first sealing element 40 being damaged or oil being blown out due to a pressure rise in the housing 4 is also eliminated.

The second sealing element 6 may, for example, be located between two rolling elements forming a rolling bearing 30 of the hydraulic machine 1, between the rolling bearing 30 and the housing 4 or between the internal volume 2 and the rolling bearing 30.

An exemplary embodiment of the second sealing element 6 will now be described with reference to fig. 3, 4 and 5. The two functions of the second sealing element 6, i.e. the sealing function and the fluid communication function, are here performed by the same component.

These figures show the second sealing element 6, here consisting of a ring 61 and an O-ring 63. The second sealing element 6 is located in a groove 7 formed at the interface between the first component 10 and the second component 20. The grooves 7 may extend radially or axially with respect to the rotation axis X-X. The examples shown in fig. 3, 4 and 5 show grooves extending radially with respect to the axis of rotation X-X. However, it should be understood that the operation is similar for the axial grooves. The structure having the axial grooves will be described below. The recess 7 is placed between the inner volume 2 and the housing 4.

The ring 61 generally forms a ring around the rotation axis X-X. It may have a rectangular cross-section (as shown in fig. 3), or a rectangular cross-section with protrusions 64 adapted to contact the walls of the first component 10 or the second component 20 (as shown in fig. 5). One or several holes 62 are formed in the ring 61, which holes 62 are adapted to allow the passage of fluid through the ring 61 and thus form the above-mentioned channels for the second sealing element 6.

Depending on the orientation of the groove 7, the thickness of the ring 61 is strictly greater than the spacing between the first component 10 and the second component 20 axially or radially around the groove 7.

In the example shown, the first and

second assemblies

10, 20 are radially separated with respect to the rotation axis X-X by a gap E1 on either side of the groove 7. Therefore, the thickness E2 of the ring 61 in the radial direction is strictly greater than E1, so that the ring 61 does not come out of the groove 7. The radial dimension of the groove 7 is strictly greater than E2 so as to allow the ring 61 and the O-ring 63 to be housed therein.

The O-ring 63 may have a circular, oval or any other cross-section. In the example shown in fig. 3, 4 and 5, the O-ring 63 has a circular section and is positioned around the ring 61, that is to say it is in contact with the ring 61 and surrounds the ring 61 radially from the outside with respect to the rotation axis X-X.

Fig. 4 shows the effect of the peak pressure in the inner volume 2.

The arrows illustrate the effect of the peak pressure on the different elements of the second sealing element 6. As can be seen in this figure, the O-ring 63 is then pressed against the axial wall of the groove 7, here the wall of the groove 7 opposite the inner volume 2. The pressure increase in the groove 7 also causes the ring 61 to be pressed under the influence of the pressure and the O-ring 63 of the compression ring 61.

The squeezing of the ring 61 causes the ring 61 to deform, thereby closing the hole 62 when the pressure is greater than the pressure threshold, thereby preventing the passage of fluid through the second sealing element 6.

It is also understood that the operation is reversible; the same function is performed in case the pressure in the housing 4 is elevated with respect to the inner volume 2. Then, the second sealing element 6 is adapted to allow fluid to flow from the housing 4 to the inner volume 2 when the pressure in the housing 4 is less than or equal to a pressure threshold (or when a pressure difference between the housing 4 and the inner volume 2 exceeds a threshold), and to isolate the housing 4 from the inner volume 2 when the pressure in the housing 4 is greater than the pressure threshold, which allows to prevent impurities from entering the inner volume 2.

Fig. 6 shows a variant of the embodiment already described with reference to fig. 2. The seal between the first component 10 and the second component 20 is ensured by the absolute seal and the second sealing element 6 as defined above.

In the exemplary embodiment, an absolute seal 8 is formed between the housing 4 and the internal volume 2 at the interface between the first component 10 and the second component 20. This absolute seal 8 isolates the housing 4 from the internal volume 2 and prevents any fluid between the two volumes from passing through the seal.

The second sealing element 6 is located in the bypass duct 60 formed in the first assembly 10 or the second assembly 20, and therefore the circulation of the fluid can be ensured in the manner of a calibrated valve or a bi-directional flow nozzle as described above.

The operation is the same as already described with reference to fig. 2 to 5.

The bypass line 60 can be formed, for example, by a bore leading to a valve which forms an external calibration valve or an external two-way flow nozzle (for example a metal valve with two lines), which here forms the second sealing element 6.

Fig. 7 shows a variant of the embodiment already described with reference to fig. 2.

In the present embodiment, the groove 7 is formed in the axial direction of the rotation axis X-X.

Thus, the second sealing element 6 extends in the axial direction, not in the radial direction. Considering the second sealing element 6 comprising the ring 61 and the O-ring 63 as described above, the ring 61 and the O-ring 63 are then stacked in the axial direction.

The operation is the same as already described with reference to fig. 2 to 5.

Thus, the proposed structure can protect the seals of the rotating machine from the effects of pressure rise within the internal volume, insufficient lubrication within the casing, and pressure rise within the casing due to heating by isolating the internal volume from the surrounding environment. The housing can thus be reduced, since it is no longer necessary for the housing to perform an oil storage and reserve function, as long as the lubrication of the first sealing element 40 is ensured by oil from the internal volume of the hydraulic machine. The hydraulic machine is more reliable, less bulky and no longer requires special maintenance of the oil in the casing.

Although the present invention has been described with reference to specific exemplary embodiments, it will be apparent that modifications and variations can be made to these examples without departing from the general scope of the invention as defined in the claims. In particular, individual features of different illustrated/mentioned embodiments may be combined in additional embodiments. The specification and drawings are, accordingly, to be regarded in an illustrative rather than a restrictive sense.

It is also obvious that all features described with reference to a method can be transposed to a device either individually or in combination, on the contrary, all features described with reference to a device can be transposed to a method either individually or in combination.

Claims

1. A hydraulic machine (1) comprising a first assembly (10) and a second assembly (20) movable in rotation with respect to each other along a rotation axis (X-X), said hydraulic machine (1) comprising a crankcase defining an internal volume (2),

wherein the interface between the fixed and movable assembly comprises a housing (4) provided with a first dynamic sealing element (40) to ensure the sealing of the inner volume (2) with respect to the external environment,

characterized in that a second dynamic sealing element (6) is located at the interface between the fixed and movable assemblies, between the inner volume (2) and the housing (4), the second sealing element (6) being adapted to allow oil to flow from the inner volume (2) to the housing (4) when the pressure deviation between the inner volume (2) and the housing (4) is less than a pressure threshold, thereby allowing fluid from the inner volume to lubricate the first sealing element (40), and not to allow oil to flow from the inner volume (2) to the housing (4) when the pressure deviation between the inner volume (2) and the housing (4) exceeds a threshold greater than the pressure threshold.

2. The hydraulic machine (1) according to claim 1, wherein the second sealing element (6) comprises a passage adapted to be closed when the pressure deviation between the internal volume (2) and the casing (4) exceeds the threshold value.

3. Hydraulic machine (1), according to claim 1 or 2, wherein said first sealing element (40) is an axial seal comprising a first metal ring (41), a second metal ring (43), a first elastic ring (42) and a second elastic ring (44), said first metal ring (41) and said second metal ring (43) being mounted against each other along an axial direction defined by said rotation axis (X-X), said first elastic ring (42) being interposed between said first metal ring (41) and said first assembly wall (14), said second elastic ring (44) being interposed between said second metal ring (43) and said second assembly wall (24) of said second assembly (20).

4. The hydraulic machine (1) according to any of claims 1 to 3, wherein the second sealing element (6) comprises an O-ring (63).

5. A hydraulic machine, according to claim 4, in which the second sealing element (6) comprises a ring (61) on which the O-ring (63) is mounted.

6. The hydraulic machine (1) according to claim 5, wherein the ring (61) comprises a hole (62) adapted to allow the passage of oil when the pressure deviation between the internal volume (2) and the casing (4) is less than or equal to the pressure threshold and not allow the passage of oil when the pressure deviation between the internal volume (2) and the casing (4) exceeds the threshold.

7. The hydraulic machine (1) according to any one of claims 1 to 6, wherein the second sealing element (6) is located between two rolling elements (32, 34) to ensure relative rotational movement between the first assembly (10) and the second assembly (20).

8. The hydraulic machine (1) according to any of the claims from 1 to 7, wherein the second sealing element (6) is made in one piece.

9. The hydraulic machine (1) according to any one of claims 1 to 8, wherein the second sealing element (6) is adapted to allow the flow of oil from the casing (4) to the internal volume (2) when the pressure deviation between the internal volume (2) and the casing (4) is less than or equal to the pressure threshold value, and to allow the isolation of the casing (4) from the internal volume (2) when the pressure deviation between the internal volume (2) and the casing (4) is greater than the pressure threshold value.

10. The hydraulic machine (1) according to any one of claims 1 to 9, wherein the second sealing element (6) is interposed between two surfaces facing each other along an axial direction defined by the rotation axis (X-X).

11. The hydraulic machine (1) according to any one of claims 1 to 10, wherein the second sealing element (6) is interposed between two surfaces facing each other in a radial direction with respect to the rotation axis (X-X).

12. The hydraulic machine (1) according to any one of claims 1 to 11, wherein the pressure threshold is equal to 0.5 bar, or more particularly equal to 0.2 bar.

13. The hydraulic machine (1) according to any one of the preceding claims, comprising: a cylinder block provided with a plurality of housings extending radially with respect to said rotation axis (X-X), in which housings cylinders are provided; and a multi-lobed cam surrounding the cylinder.